Williams has recovered more than 9,000 gallons of natural gas liquids at its leak site near Parachute Creek north of Parachute, which is about 90 percent of what it believes entered soil and groundwater.

The Colorado Department of Public Health and Environment said in an update Friday that the remediation efforts are proving successful, having reduced a benzene-containing groundwater plume by about 200 feet, and on average cutting benzene concentrations by about half in that plume, except in the immediate vicinity of the leak source.

That source was a burst valve pressure gauge on a pipeline leaving a Williams gas processing plant. Williams believes about 50,000 gallons leaked, but that all but 10,000 gallons vaporized before reaching the ground.

At its Answers for Parachute website, the company says it had recovered 9,147 gallons of natural gas liquids as of Jan. 13. It removed more than 1,000 gallons over the course of one month alone late last year.

Benzene, a carcinogen, reached Parachute Creek for a time last year, briefly going just above the 5 parts per billion level that’s the designated safe drinking water standard, although the creek isn’t considered a drinking water source. However, no benzene has been detected in the creek since August.

Williams has used measures ranging from aeration-based systems, to removal, treatment and reinjection of groundwater, to try to clean up the aquifer. State health officials say that thanks to such efforts, the number of monitoring wells containing liquid hydrocarbons has fallen to five, from 10 last May.

Benzene concentrations fell from the 40- to 1,000-ppb-range to non-detect downgradient of one remediation system, and from 720-2,400 ppb to less than 50 ppb downgradient of another.

However, pockets of higher concentrations have lingered. As of late November, one monitoring point in the immediate area of the leak source had 68,000 ppb of benzene.

The department of health and environment said current operations and monitoring will continue unchanged because of their effectiveness.

In mid-February, Williams is scheduled to submit a final “Corrective Measures Work Plan” describing any technologies it want to use to complete the cleanup.

The Hydrocarbon Recovery System (HRS) has been in operation since August and has recovered an estimated 279 gallons (6.6 barrels) of liquid hydrocarbons.

Approximately 1,755 gallons (42 barrels) of liquid hydrocarbons have been recovered from recovery wells.

9,147 gallons (approximately 218 barrels) total from the site.

A total of 1,852 tons of contaminated soil have been disposed of at the ECDC Landfill in East Carbon, Utah, and soil pile disposal is complete.

Approximately 2,759 gallons of liquid hydrocarbon have been shipped off-site for recycling.

221,600 gallons of staged water have been treated and discharged under permit to an infiltration gallery.

Williams continues to work with the Colorado Department of Public Health and Environment, United States Environmental Protection Agency, and Colorado Oil and Gas Conservation Commission to develop long term remediation plans.